This invention pertains to threaded retention pins used in restorative dentistry for enhancing the attachment of an amalgam or other restorative material on the tooth. Well known retention pins of this general type are externally threaded and are inserted by rotation into a previously-drilled pinhole which extends into the dentin of the tooth structure. Rotation of such a pin cuts internal threads in the pinhole and advances the pin longitudinally into the pinhole. When the pin is sufficiently inserted, a driving head at the upper end thereof is sheared from the pin by a self-shearing joint, leaving an upper portion of the retention pin in the restoration cavity where the restorative material is placed thereabout.
I have recognized heretofore that retention pins which do not have thread cutting edges produce crazing of the dentin. This is averted to some extent by the structure shown by thread cutting U.S. Pat. No. 3,861,043 in which edges are provided at the extreme lower end of a short slot retention pin. I have informed others in publications made in 1973 and 1974 that crazing would be reduced by a retention pin resembling a machinist's tap, having peripheral threads interrupted by longitudinal grooves. The present invention pertains to improvements in such proposed retention pins, such improvements pertaining in part to the provision in the pin of a pinhole-sealing section which seals against the interior wall of the pinhole and substantially prevents the entry of fluid into the groove or grooves located within the pinhole. The invention also pertains to a method of preparing a restoration cavity by the use of such an improved retention pin.
This invention has as its objectives the provision of a retention pin and method of use which reduces the crazing of the dentin while at the same time becoming affixed securely to the tooth and preventing the entry of fluids into the pinhole once the retention pin is in position.
According to this invention, the retention pin includes an externally threaded lower shaft having a vent passage for releasing fluid from the pinhole as the lower shaft portion is inserted. A pinhole sealing portion is located at the upper end of the lower shaft portion and has a peripheral sealing surface which engages the pinhole surface to prevent fluid from entering the pinhole when the lower shaft portion is fully inserted in the pinhole. An upper shaft portion extends upwardly from the pinhole-sealing portion for embedment in restorative material placed in the restoration cavity.
The method of this invention involves the drilling of a pinhole of a given diameter, inserting an externally threaded lower end of a retention pin in the pinhole by rotation, the lower end being provided with threads having a crest diameter greater that the pinhole diameter. During such rotation, fluid is vented from the pinhole to prevent compression, and threads are cut in the pinhole by moving thread-cutting edges on the pin into the wall of the pinhole. During the final stages of the insertion step, a sealing portion of the pin is moved into the pinhole, such sealing portion having a diameter substantially equal to the pinhole diameter.
For a more complete understanding of this invention, reference is made to the accompanying drawings and the following description of a preferred embodiment.